全文获取类型
| 收费全文 | 75766篇 |
| 免费 | 12081篇 |
| 国内免费 | 16934篇 |
专业分类
| 测绘学 | 5488篇 |
| 大气科学 | 7876篇 |
| 地球物理 | 12678篇 |
| 地质学 | 44364篇 |
| 海洋学 | 9596篇 |
| 天文学 | 7345篇 |
| 综合类 | 5312篇 |
| 自然地理 | 12122篇 |
出版年
| 2024年 | 260篇 |
| 2023年 | 828篇 |
| 2022年 | 2071篇 |
| 2021年 | 2408篇 |
| 2020年 | 2438篇 |
| 2019年 | 3145篇 |
| 2018年 | 2423篇 |
| 2017年 | 2679篇 |
| 2016年 | 2944篇 |
| 2015年 | 3201篇 |
| 2014年 | 4155篇 |
| 2013年 | 4066篇 |
| 2012年 | 4524篇 |
| 2011年 | 4899篇 |
| 2010年 | 4400篇 |
| 2009年 | 5192篇 |
| 2008年 | 4986篇 |
| 2007年 | 5458篇 |
| 2006年 | 5216篇 |
| 2005年 | 4569篇 |
| 2004年 | 4325篇 |
| 2003年 | 4041篇 |
| 2002年 | 3517篇 |
| 2001年 | 3191篇 |
| 2000年 | 2902篇 |
| 1999年 | 2680篇 |
| 1998年 | 2272篇 |
| 1997年 | 1963篇 |
| 1996年 | 1784篇 |
| 1995年 | 1492篇 |
| 1994年 | 1443篇 |
| 1993年 | 1254篇 |
| 1992年 | 997篇 |
| 1991年 | 717篇 |
| 1990年 | 573篇 |
| 1989年 | 505篇 |
| 1988年 | 345篇 |
| 1987年 | 223篇 |
| 1986年 | 171篇 |
| 1985年 | 131篇 |
| 1984年 | 60篇 |
| 1983年 | 58篇 |
| 1982年 | 57篇 |
| 1981年 | 33篇 |
| 1980年 | 35篇 |
| 1979年 | 34篇 |
| 1978年 | 45篇 |
| 1977年 | 30篇 |
| 1975年 | 4篇 |
| 1954年 | 15篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
91.
胶东“玲珑-焦家式”金矿资源潜力与找矿 总被引：1，自引：1，他引：0
“玲珑焦家式”金矿的成岩成矿,从新太古代至中生代存在着继承性的成因关系,成矿具有长期性、多源性特点,但中生代燕山早期岩浆活动是主导成矿因素。区域化探成果显示胶东金矿直接矿源岩———郭家岭花岗岩金的丰度比原始矿源岩———早前寒武纪变质沉积岩系及侵入岩系金的丰度低1/2。郭家岭花岗岩面积在2 km2以上岩体定量估计金亏损总量与胶东金矿总量预测的资源量相当,从一个侧面展现了胶东金矿资源的潜力。望儿山金矿的找矿实践展示,焦家式金矿在1 000 m以下尚有巨大潜力,整个胶东金矿产区在3 000 m以上的资源潜力应在5000 t以上。 相似文献
92.
MEN Wu ) WEI Hao ) and LIU Guangshan ) * ) College of Oceanography Environmental Science Xiamen University State Key Laboratory of Marine Environmental Science 《中国海洋大学学报(英文版)》2006,5(3):228-234
1Introduction Therearefourradiumisotopesinnature,ofwhich224Ra,226Raand228Rahavebeenwidelyinvestigated inmarineresearch,butthespecificactivityof223Rais toolowtobemeasured,therefore,itsapplicationsarelimited(Moore,1969;Broeckeretal.,1976;KuandLin,1976;Nozak… 相似文献
93.
上扬子地台震旦系铅锌矿床类型及找矿方向 总被引：13，自引：0，他引：13
上扬子地台含铅锌矿地层主要为震旦系。震旦系在上扬子地台主要发育上统灯影组,次有下统陡山沱组。将上扬子地台震旦系铅锌矿床成因划分为一级为叠生矿床,二级为层控矿床,三级为热水沉积改造矿床和热水沉积再造矿床四级类型,该类型按铅锌比例进一步划分为富铅型、富锌型、铅锌共生型。研究区内最重要的铅锌矿床成因类型为南郑马元、会东大梁子铅锌矿为代表的富锌型。陕西南郑、紫阳—镇坪地区,湖北武当、神农架、黄陵地区,以及地台西缘的安宁河、甘洛—小江、峨边—寻甸等地区的震旦系是寻找铅锌矿的最有利地段。 相似文献
94.
95.
96.
The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
97.
98.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
99.
100.